Top 5 Most Damaging Invasive Species in the U.S.

Animal invaders have bridged oceanic gaps for centuries—some stowed away in ship-ballast water while others were intentionally lugged over by the overzealous, either to solve a pre-existing problem or just for aesthetic pleasure. However, sometimes a seemingly benign introduction creates environmental travesty and ecosystem despair. Here are the most damaging animals ever to enter U.S. soil.

Starlings

Starlings

"Invasive species have been a problem as long as America has existed as a nation," says Thom Cmar of the Natural Resources Defense Council (NRDC). However, Cmar says that as transportation into the country has become more advanced, more invasive species have come in on boats and planes, thus worsening the problems posed to ecosystems.

These species have the uncanny knack of muscling out local competitors in the U.S., sometimes pushing commonplace species onto the endangered list by outcompeting them for food or resources. And as these creatures perpetually vandalize ecosystems, the U.S. has to shell out the money to fix the messes and restore nature's balance. Removing organisms that are numerous and evasive is no easy task, similar to finding a needle in a haystack, and so the U.S. focuses its efforts on border patrol, ensuring that no more of these species enter the country.

The NRDC advocates closing the routes that invasive species often use to hitchhike into the country, while the U.S. Fish and Wildlife Service, under the Lacey Act, regulates what people are legally allowed to bring in to the U.S.

"The costs of invasive species are so high, literally hundreds of billions of dollars a year," Cmar says. "Allowing these species to continue to come in and devastate our economy and ecology isn't an acceptable solution."

Of all the invaders, here are the worst of the worst, those that seem to be guests in the U.S. for the long haul, regardless of plans devised to be rid of them.

Constrictors

Constrictors

Big constrictors squeeze the life out of mammalian prey and ecosystems. The U.S. Geological Survey says nine species of pythons, a type of snake that can range from 12 to 28 feet in length, pose a medium- to high-risk threat to ecosystem health. Over the past 30 years, these weighty reptiles have been traded domestically and internationally, and pet owners often take these snakes into homes that cannot accommodate them as they grow. When the snakes get too big, offending owners release them into the typically Floridian wild, where they ingest endangered species like the Key Largo wood rat and invade wildlife refuges. Under the Lacey Act, the U.S. Fish and Wildlife Service proposed to stop constrictor serpent imports into the country and even ban transport between states.